The window doesn't have a correct "layout" and if I resize it the form doesn't adapt to it.
Am I doing something wrong? If I remove the config word and set all configuration properties in the defines configuration everything works as expected.

Another "strange" problem that has no workaround is when declaring window buttons:

Below is a simple window extension which also addresses the button scope issue. Note that I assigned a widget alias of 'mw' to the extended Window, which you can then use with Ext.ComponentQuery, up(), down(), etc.